This invention relates to apparatus and methods for the treatment of body lumens, and particularly to delivery systems for endoprostheses. More particularly, the invention relates to biocompatible and/or bioabsorbable sheaths for self-expanding stents. The present invention also is directed to a delivery system for self-expanding stents which facilitates minimal stent movement during deployment to achieve more accurate stent placement within the patient""s vasculature.
Several interventional treatment modalities are presently used for heart disease including balloon and laser angioplasty, atherectomy and by-pass surgery. In a typical cardiovascular intervention, a guiding catheter having a preformed distal tip is percutaneously introduced over a first wire, such as a 0.035xe2x80x3 wire, that has been placed in the vasculature through a guiding sheath into an artery and advanced within the cardiovascular system until the distal tip of the guiding catheter is seated in the ostium of a coronary artery. The first wire is removed and a guidewire, such as a 0.014xe2x80x3 guidewire, is advanced distal to the treatment area. Then a dilatation catheter is back-loaded onto the guidewire and tracked to the treatment area through the guiding catheter. Once in position across the lesion, the balloon is inflated to a predetermined size with radiopaque liquid at relatively high pressure (e.g., greater than four atmospheres) to compress the plaque of the lesion and to otherwise expand the inner lumen of the artery.
Further details of dilatation catheters, guidewires, and devices associated therewith for angioplasty procedures have been known for a number of years, and by way of example, several forms of such devices can be found in U.S. Pat. No. 4,323,071 (Simpson-Robert); U.S. Pat. No. 4,439,185 (Lindquist); U.S. Pat. No. 4,516,972 (Samson); U.S. Pat. No. 4,538,622 (Samson, et al.); U.S. Pat. No. 4,554,929 (Samson, et al.); U.S. Pat. No. 4,616,652 (Simpson); U.S. Pat. No. 4,638,805 (Powell); U.S. Pat. No. 4,748,982 (Horzewski, et al.); U.S. Pat. No. 5,507,768 (Lau, et al.); U.S. Pat. No. 5,514,154 (Lau, et al.); U.S. Pat. No. 5,451,233 (Yock); and U.S. Pat. No. 5,458,615 (Klemm, et al.); and U.S. Pat. No. 5,700,286 (Tartaglia, et al.).
A focus of recent development work in the treatment of heart disease has been directed to endoprosthetic devices called stents. Stents are generally cylindrically shaped intravascular devices which are placed within an artery to hold it open. The device can be used to reduce the likelihood of restenosis and to maintain the patency of a blood vessel immediately after intravascular treatments. In some circumstances, they can also be used as the primary treatment device where they are expanded to dilate a stenosis and then left in place.
Prior art stents typically fall into two general categories of construction. The first type of stent is expandable upon application of a controlled force, often through the inflation of the balloon portion of a dilatation catheter which, upon inflation of the balloon or other expansion means, expands the compressed stent to a larger diameter to be left in place within the artery at the target site. The second type of stent is a self-expanding stent, which may be formed from shape-memory metals such as super-elastic nickel titanium (NiTi) alloys which will automatically expand from a compressed state when the stent is advanced out of the distal end of the delivery catheter into the body lumen. Such self-expanding stents can typically be expanded without the need for application of a controlled force on the stent, such as is applied through the inflation of the balloon portion of a dilatation catheter. Such self-expanding stents may be manufactured from expandable heat-sensitive materials that allow for phase transformation of the materials to occur at set temperatures, resulting in the expansion and/or contraction of the stents.
One method and system developed for delivering stents to desired locations within the patient""s body lumen involves advancing the stent delivery system through the patient""s vascular system until the stent is positioned within the treatment area, and then inflating the expandable member on the catheter to expand the stent within the blood vessel. The expandable member is then deflated and the catheter withdrawn, leaving the expanded stent within the blood vessel, holding open the passageway thereof. This approach is common with stents of the first type, i.e., stents that are not self-expanding.
Implanting self-expanding stents within the patient""s vasculature often require different methods than the one set forth above for non-self-expanding stents. Some prior art stent delivery systems for self-expanding stents include a catheter with an inner lumen upon which the compressed or collapsed stent is mounted, and an outer restraining sheath which is eventually placed over the compressed stent prior to deployment. When the stent is to be deployed in the body vessel, the outer sheath is moved in relation to the inner lumen to xe2x80x9cuncoverxe2x80x9d the compressed stent, allowing the stent to move to its expanded condition. Some delivery systems utilize a xe2x80x9cpush-pullxe2x80x9d technique in which the outer sheath is retractable while the inner sheath is pushed forward or held in place. Still other systems use an actuating wire which is attached to the outer sheath. When the actuating wire is pulled to retract the outer sheath over the collapsed stent, the inner lumen must remain stationary, preventing the stent from moving axially within the body vessel.
Because proper positioning of the stent is critical to the performance of the stent, it is imperative that the physician knows exactly where the stent will be placed upon deployment.
What has been needed and heretofore unavailable is an improved device and method for accurately providing for release and deployment of stents, including self-expanding stents. The present invention satisfies these and other needs.
Briefly, and in general terms, the present invention is directed to a bio-compatible or bio-absorbable addition to a stent and/or stent delivery system. More particularly, the invention relates to a bio-compatible or bio-absorbable sheath, lining, or filament positioned on or in a stent. The bio-compatible or bio-absorbable material is designed to be implanted in the body along with the stent. After implantation, the material may be absorbed into the body, such as where the material is a bio-absorbable material that dissolves over a period of time.
In one embodiment of the invention, a bio-absorbable or bio-compatible filament is wound through or around an expandable stent. The filament may have sufficient strength to help in constraining the stent in an unexpanded configuration. Such a filament may still have sufficient weakness to permit the stent to be expanded via the application of a force, such as via the application of force provided by the expansion of a balloon catheter where the stent is positioned on the balloon. Expansion of the stent may be achieved by applying sufficient force to cause the filament to break or otherwise fail or relax. Expansion of the stent may be achieved by changing the configuration of the filament, such as by pulling or pushing, proximally or distally, on the filament until it no longer provides sufficient restraint to prevent the stent from expanding. The filament may be formed from various materials, including polymers. The filament may comprise one or more therapeutic agents, such as a drug useful in treating arterial walls.
Such a filament may be bonded to the delivery catheter and/or the stent, such as where a polymer filament is heat-bonded in a tightly-coiled position around the stent. During stent deployment, which may be achieved through inflation of a balloon catheter, the bonding of the filament to the stent and/or delivery catheter may fail, in whole or in part, loosening the tightness of the filament around the stent and permitting the stent to expand.
The filament maybe used to constrain self-expanding stents to prevent their expanding prior to the desired time and position for stent deployment. The filament may also be used with non-self-expanding stents, such as balloon-expandable stents, to help to retain the stent on a delivery system, such as a delivery catheter. The filament may also comprise and/or be used to deliver therapeutic agents, such as drugs or radiation therapy materials, or other materials that improve stent delivery, deployment, and/or performance, including materials that improve stent visibility under fluoroscopy or that facilitate radiation therapy.
In a further embodiment of the invention, the bio-compatible and/or bio-absorbable material forms a sheath and/or coating that surrounds the stent, in whole or in part. Like the filament, the sheath and/or coating may have sufficient strength to help in constraining the stent in an unexpanded configuration, and may still have sufficient weakness to permit the stent to be expanded by applying sufficient force to cause the sheath to break or otherwise fail and/or relax. The sheath and/or coating may be formed from various materials, including polymers, and may comprise one or more therapeutic agents. In the case of a coating that is bonded to the stent, the coating may be applied to the inner or outer surface of the stent.
In a further embodiment of the invention, the bio-compatible and/or bio-absorbable material is positioned in openings in the stent itself. For example, the material may be positioned to fill one or more of the openings in an expandable stent pattern. In stents that require such openings to change shape during stent expansion, the material may serve to prevent stent expansion by preventing the openings from changing shape. For example, the material may serve as an adhesive that holds the sides of the opening in close proximity to one another, thereby preventing the stent from expanding. The material maybe configured to fail or otherwise relax when sufficient force is applied to expand the stent, such as the force applied by inflation of a catheter balloon.